(1) Field of the Invention
This invention relates to a novel agent for coloring seeds (will hereinafter be called "seed colorant"), and more specifically to a novel seed colorant having excellent adhesion to various seeds and giving good influence to the germination percentage and growth of the seeds.
(2) Description of the Prior Art
A variety of seeds such as cereals has heretofore been used in an enormous quantity for foods. Of these seeds, those to be used for seeding have been subjected to various disinfection and other chemical treatments. Their accidental use for foods is hence very dangerous. In view of this, seeds to be used for seeding are often colored in various hues so as to indicate clearly that they are for seeding.
Employed routinely as such seed colorants are those obtained by either dissolving or dispersing a dye and/or pigment in a solution of a binder resin. Regarding such a binder resin, an emulsified hydrophobic vinyl resin or a water-soluble resin is used as a synthetic binder resin by way of example. In addition, natural water-soluble resins are also used widely.
The following properties are required for such binder resins. First of all, they are not supposed to give any deleterious effects to seeds. As a second requirement, they must have sufficient adhesion to seeds.
Where an emulsion of a hydrophobic synthetic resin is used as such a binder resin for seeds, it has good adhesion to the seeds. It however involves a potential danger of giving adverse effects to the germination and growth of the seeds, because one or more monomers still remain in the emulsion and a surfactant is also used in combination in the emulsion. It is also desirable that the binder resin would be biodegraded promptly subsequent to seeding. Such a hydrophobic synthetic resin is however accompanied by a further drawback that it has poor biodegradability.
On other hand, water-soluble synthetic binder resins such as polyvinyl alcohol are free of such monomer- and surfactant-related problems. However, they are also accompanied by a drawback that their biodegradability is poor. Further, they are highly hygroscopic and are therefore inferior in adhesion. They are accompanied by a further problem that seeds are caused to get together since seed surfaces become sticky as a result of absorption of moisture.
Further, water-soluble natural binder resins such as cellulose derivatives, gelatin and casein have superb biodegradability but similar to the above-mentioned resins, they are inferior in the adhesion to seeds and other properties.
As a coloring agent, it is preferable to use a pigment having excellent fastness. This pigment is however inferior in the stability of its dispersion in a solution of such a binder resin, and therefore is not equipped sufficient stability as a coloring agent.
It has hence been desired to develop a novel seed colorant which does not have any adverse effects to seeds, can exhibit good adhesion to the seeds, has excellent biodegradability and is superb in the stability of dispersion of its pigment or pigments.